How to remove limescale from your heating system
- ross milne
- Jun 22
- 5 min read
Updated: Jun 26
Let’s be honest — if you’ve got hard water, you’re probably already battling limescale daily. It takes over your kettle, clouds your shower, and glues itself to your taps like a bad house guest. But one of the worst places for it to build up? Deep inside your heating system — where you can’t see it, but definitely feel the effects.
Over time, that hidden limescale can mess with your boiler’s efficiency, slow down your radiators, hike up your bills, and even cause breakdowns. The good news? You don’t need to rip everything out and start again. Here’s how to clear out the scale — and stop it coming back — without losing your cool (or your central heating).
What exactly is limescale doing to your heating system?
Limescale is made of calcium carbonate, a mineral found in hard water. When water is heated, this mineral comes out of solution and sticks to surfaces — especially metal parts like your boiler’s heat exchanger or immersion heater.
That chalky build-up acts like insulation where you don’t want it. Your boiler has to work harder to heat water, radiators might take longer to warm up, and hot water flow can slow to a trickle. It’s also a common cause of noise in boilers — if yours is making a banging or kettling sound, limescale could be the problem.
How to remove limescale from your heating system
If you suspect your system is suffering from scale, here are a few ways to clear it out. Always read the instructions carefully and check it’s suitable for your specific setup — especially if you have an older boiler.
Chemical descaler (DIY or pro)
You can buy central heating system descalers that circulate through your pipes and dissolve built up limescale. These are added to the system via a radiator or filling loop and left to work before flushing out. Some are designed for DIY use, but it’s worth getting a heating engineer to do this task if you’re not confident.
Look for a central heating descaler that’s compatible with your system, safe for metals and seals in your boiler and BS7593-compliant (the British Standard for water treatment).
Brands like Fernox and Sentinel all offer well-reviewed products.
Fernox F3 Cleaner
Sentinel X800 Fast Acting Cleaner
You'll also want to grab yourself one of these:
Just Dose It Central Heating Dosing Tool
Power flushing
This is a more heavy-duty option, where a heating engineer connects a powerful pump to your system and flushes out sludge, scale, and debris using a mix of chemicals and water. It’s effective — and can sometimes rescue a system that’s on its last legs — but it’s not cheap — we’re talking hundreds, or if you have a big house, thousands of pounds. But it will help your system run efficiently again which should reduce your energy bills.
It’s also only suitable for certain types of heating systems and boilers, so always get a proper assessment from a professional heating engineer first.
A quick note on power flushing and the environment...
Power flushing isn’t the greenest job — it uses a lot of water and chemical cleaners, and the waste can contain sludge, rust, and other nasties. But if your system is seriously suffering, a power flush can make it run far more efficiently, helping your boiler use less energy and last longer. That means fewer repairs, lower bills, and less environmental impact over time.
If you're eco-conscious, ask your heating engineer about using low-toxicity or biodegradable cleaners, and make sure they dispose of the flush water responsibly. Adding a magnetic filter and keeping inhibitor levels topped up can also help you avoid needing another flush any time soon.
Magnetic filters and scale reducers
Once your system is clean, it’s worth adding protection to keep it that way. A magnetic system filter (often fitted near the boiler) catches metal particles and sludge, while a scale reducer (usually installed on the cold feed to your boiler or cylinder) helps prevent limescale from forming in the first place.
Neither of these removes existing scale, but they can extend the life of your system and keep things running smoothly after treatment.
What about combi boilers?
Combi boilers are especially prone to limescale build-up because they heat water directly on demand. This means water doesn’t sit in a tank — it flows straight through heat exchangers where minerals can cling and form scale.
Some combis include built-in filters or scale protection, but most still benefit from a descaler or inhibitor. If you’re installing a new one, ask your engineer about preventative options from the get-go.
Signs your heating system might be suffering from scale
Not sure if scale is the issue? Look out for these:
Radiators are slow to warm up, especially at the bottom
Your boiler makes kettling or banging noises
Hot water pressure seems lower than usual
Your boiler keeps shutting down or showing error codes
You live in a hard water area and haven’t used any treatment
How to prevent limescale build-up in future
Once you’ve cleared out the scale, here’s how to keep it from coming back:
Use a heating system inhibitor
These are chemical treatments you add to the water in your heating system to protect against both scale and corrosion. They should be topped up whenever the system is drained (e.g. for radiator replacement or maintenance).
Fit a scale reducer
These come in various forms — from electrolytic and magnetic devices to phosphate-based filters. They don’t remove minerals, but they can reduce how much sticks to your boiler and pipes.
Install a water softener
This is the gold standard for serious hard water areas. A softener removes the minerals that cause limescale altogether, protecting not just your heating but every tap and appliance in the house. They’re more expensive, but if you’re already replacing a boiler or dealing with constant scale, it can be worth it.
Why this matters more than you might think
It’s easy to ignore what’s going on behind the scenes in your heating system — until it stops working. Limescale silently shortens the life of your boiler, wastes energy, and pushes up your bills. Tackling it head-on with the right treatment and protection can save you hassle, money, and chilly mornings.
✨ Limescale Lowdown ✨
Limescale forms when hard water is heated, leaving mineral deposits on pipes and boiler components.
It reduces efficiency, slows radiator heating, and can damage your boiler over time.
Descalers (DIY or professional) can clear the build-up inside your system.
Magnetic filters and inhibitors help prevent future scale and sludge.
A water softener offers the best long-term protection in hard water areas.
